High speed and high performance network access are needed in many areas where wired infrastructure is non-existent, outdated, or impractical. Fixed wireless broadband networks can fulfill this need. However, use of existing fixed wireless broadband technology is limited due to a combination of technological constraints and high deployment costs. For example, Wireless Local Area Network (WLAN) technology requires multiple access points where each access point must be connected via cable to a wired backbone infrastructure. As a result, the network becomes difficult and costly to deploy.
To address these problems, wireless mesh network architecture has been studied as a system for becoming part of the network infrastructure and providing wireless access to users. However, wireless mesh networking is limited by its network capacity due to the requirement that nodes forward each other's packets. For example, a uniform random network with random traffic pattern has an end-to-end throughput of 1/n1/2, wherein is the total number of nodes. Therefore, throughput approaches zero as the number of nodes increase.
There are two fundamental reasons that result in diminished throughput. First, current 802.11 Media Access Control (MAC) protocol is inefficient and unfair in multi-hop environments. For example, 802.11 radios cannot transmit and receive at the same time; 802.11 MAC protocol does not correctly solve hidden terminal problems in a mesh; and Request to Send (RTS)/Clear to Send (CTS) scheduling along a multi-hop chain can cause Transmission Control Protocol (TCP) fairness problems and back-off inefficiencies. Second, only a small portion of the available spectrum is used. For example, 802.11b/g has three non-overlapping channels and 802.11a has twelve non-overlapping channels, but 802.11 is designed to use only a single channel frequency at any given time.
In the past, one possible solution was to improve the 802.11 MAC layer. However, this would require changes to the MAC and hardware, which would be expensive and take a significant amount of time to complete.
Alternatively, network capacity can be increased by using multiple radios and multiple channels. For example, a link layer protocol called the Multi-radio Unification Protocol (MUP) has been proposed to coordinate the operation of multiple wireless network cards tuned to non-overlapping frequency channels. However, there is inefficient use of available frequencies because all the nodes in the network use the same fixed channels to talk to their neighbors. As a result, no frequency reuse is available. Furthermore, same-radio packet relay, or the inability to transmit and receive packets at the same time, cannot be completely avoided.